Triacylglycerols (TAGs) are the main constituent of edible fats and oils. TAGs are composed of three fatty acids esterified onto a glycerol backbone. Fatty acids are usually linear molecules composed of long aliphatic carbon chains that can range from four to twenty-two carbons in length. Fatty acids can be saturated or unsaturated. When a fatty acid is saturated, it means each carbon atom is attached to another carbon atom via a single covalent bond. Fats and oils containing predominantly saturated fatty acid will be solid at room temperature. Examples of saturated fats include animal fat such as milk fat or lard and tropical oils such as palm oil, palm kernel oil and coconut oil. A fatty acid is unsaturated when carbon-carbon double bonds are present within the chain of carbon atoms. A carbon-carbon double bond can adopt one of two conformations, namely cis and trans. Fats and oils containing unsaturated fatty acids with cis double bonds are usually liquid at room temperature. Examples of unsaturated fats include vegetable oils such as soybean, canola and cottonseed oils. Fats and oils containing unsaturated fatty acids with trans double bonds, on the other hand, are solid at room temperature. The difference between a fat and an oil is subtle. Generally, if the melting point of the TAGs is higher than about 30° C., the material is solid at room temperature, and is therefore referred to as a ‘fat’. On the other hand, if the melting point of the TAGs is lower than about 15° C., the material will appear liquid at room temperature, and will thus be referred to as an ‘oil’. Natural fats and oils are complex mixtures of TAGs with extremely varied chemical compositions.
Unsaturated fatty acids are generally in the cis conformation. However, when an oil is partially hydrogenated, various amounts of the cis form are converted to a more stable trans configuration, and are thus called trans fatty acids. Hydrogenation is a process by which a hydrogen molecule is added to an unsaturated double bond. Hydrogenation is a way of making vegetable oils harden at room temperature. Small particles of nickel or copper catalyst are added and the mix is heated to high temperatures under pressure and agitation for up to eight hours while hydrogen gas is injected. From the time the British patent on liquid phase hydrogenation was issued to Norman in 1903, and its introduction in the U.S. in 1911, few chemical processes have made as great an economic impact on any industry. Hydrogenation opened new markets for vegetable oil based on specialty products. Three reactions take place during hydrogenation—the saturation of carbon-carbon double bonds, the conversion of cis geometric isomers into more stable trans isomers, as well as the creation of new positional isomers, where double bonds are shifted to new positions along the fatty acid chain. Both the saturation of double bonds as well as the cis to trans isomerization of double bonds will result in an increase in the melting point of a fat. Thus, cooling of this hydrogenated fat below the melting point of the newly created triacylglycerol species containing saturated and trans fatty acids, will lead to the partial crystallization of the material. This semisolid fat matrix will therefore be structured as a network of fat crystal aggregates with liquid oil trapped within. The solid-like characteristics of this material are due to this underlying fat crystal network. Without this network of crystallized fat, the material would be an oil.
Manufacturers use the hydrogenation process to convert vegetable oil into a solid form for the manufacture of margarine, shortening and spreads. The process is also used to increase the shelf life and flavor stability of food products containing vegetable oils. During hydrogenation, anywhere from eight to seventy percent of the fatty acid content will be converted to trans fatty acids. The amount of conversion depends on the process and the desired product.
Trans fatty acids also occur naturally. When unsaturated fatty acids are ingested by ruminants (i.e., cows) the fatty acids can be partially hydrogenated by bacteria in the rumen of the animal (stomach) and thus trans fatty acids can be found in milk fat, dairy products, beef and mutton fat. Trans fatty acids usually make up about two to nine percent of the fat in these products. Ruminant animals are not the only animals in which this process occurs. Chicken and pigs often ingest trans fatty acids through the feed they are given and the trans fatty acids make their way into pork and poultry products.
Over the past 50 years hydrogenated oils have become a prevalent part of the diet in developed countries. Margarine is an example of a product that contains hydrogenated oils and it is one of the most common sources of hydrogenated oil in our diets. These hydrogenated oils have become so commonplace in prepared foods that it is a major feat to avoid them. Margarine is sometimes marketed as a healthy alternative to saturated fats like butter and lard. However while these products start out as unsaturated oils, the final product includes trans fatty acids that are increasingly under attack as major contributors to cardiovascular disease.
New research into the role fats and oils play in human health has indicated that consumption of trans fatty acids is associated with increased incidences of cancer, heart disease, elevated cholesterol levels and a host of other health problems. Over ten years of clinical and epidemiological research suggest that there is a positive linear relationship between trans fatty acid intake and a decrease in serum HDL (‘good’ cholesterol) combined with an increase in serum LDL (‘bad’ cholesterol). These combined effects increase the risk of coronary heart disease. Both the Institute of Medicine and the American Heart Association recommend a reduction in the intake of trans fatty acids, and to preferably eliminate them altogether from the diet. This is difficult to achieve without proper labeling of foods. Prompted originally by the Center for Science in the Public Interest back in 1994, the U.S. Food and Drug Administration (FDA) has decreed that, as of January of 2006, food manufacturers must include the trans fatty acid content in product labels.
Long before the health risks associated with trans fatty acids were realized, it was known that consumption of animal fats and tropical oils had a negative effect on cardiovascular health. The American Heart Association (AHA) discourages the consumption of animal fats such as butter (milk fat), lard (pig fat), tallow (beef fat) due to their relatively high content of cholesterol and saturated fatty acids, which makes them highly atherogenic—they contribute to the build up of cholesterol and other substances in artery walls. The AHA also discourages the consumption of trans fats. Moreover, the AHA also discourages the consumption of tropical oils such as palm oil, palm kernel oil and coconut oil due to their high saturated fatty acid content.
The need for a healthy alternative to trans fatty acids and saturated fats creates technological hurdles for the food manufacturing industry. It is difficult to eliminate trans fats from a food formulation where the goal is to transform an oil, which is liquid at room temperature to a fat, which is ‘solid’ at room temperature to enhance texture and appearance of a food product.
There have been various attempts in the food industry to provide an edible oil product that is solid at room temperature and that contains little or no trans fatty acids or saturated fats. For example, U.S. Pat. No. 6,569,478 discloses a food composition comprising at least one food ingredient in a monoglyceride mix in an amount sufficient to form a mesomorphic structure which substantially encapsulates the food ingredient and water.
U.S. Pat. No. 6,156,369 discloses a food spread comprising a non-aqueous mixture of an edible oil and a monoglyceride in an amount of from about 85% to about 98% edible oil and from about 2% to about 15% monoglyceride.
Canadian Patent No. 2,096,429 discloses a finished foodstuff comprising bulk regions of a mesomorphic phase of edible surfactant and less than 80 wt % edible oil, and wherein the mesomorphic phase is a continuous phase and/or contains 80 wt % or more of water as well as methods of making and using the foodstuff.
Much of the effort to create low-trans and saturate fat alternatives has focused on the use of monoglyceride gels. The early work on monoglyceride gels focused on aqueous lyotropic systems only. When heated above their ‘Kraft’ temperature, monoglycerides and other amphiphillic molecules, can form lamellar phases structured as alternating layers of monoglyceride bilayers and water. Upon cooling, monoglycerides will crystallize into kinetically favored, but thermodynamically metastable forms, yielding an alpha-gel. This alpha-gel is structured in a similar fashion as the lamellar phase—water layers sandwiched between monoglyceride bilayers. Upon ageing, alpha-gels tend to rearrange into beta-gels, or coagels, upon transformation of monoglyceride crystals into more thermodynamically stable crystal forms. In these coagels, however, water layers are squeezed out of the gel structure, leaving behind stacked monoglyceride bilayers.
These mesophases (alpha-gels and coagels) were the subject of a flurry of research activity and several patents by Unilever R&D. In all of this work, aqueous mesophase gels—, usually of water contents greater than 80%—were mixed with a variety of materials for structuring purposes. Under vigorous mixing (high shear), aqueous mesophase gel material was dispersed within other phases until some kind of stabilization was achieved. This method of making monoglyceride gels limited this technology to the manufacture of low-fat edible spreads. Monoglycerides can also be used to structure pure oil, but in that case, monoglycerides are used as a conventional hardstock, and not as a mesophase gel.
Using standard techniques of blending, interesterification (chemical and enzymatic) and fractionation, it is virtually impossible to produce a spread having the texture of a tub-type margarine without incorporating saturated fats and/or trans fatty acids. Thus, there has long been an unmet need for alternative technologies to provide a product that has the consumer desired features of texture and spreadability without harmful trans fats, animal fats and tropical oils.